FIELD OF THE INVENTION
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The invention generally relates to computer networks and, more particularly, the
invention relates to a system and method of supporting a label switched path across a non-MPLS
compliant segment of a communication network.
BACKGROUND OF THE INVENTION
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Typically, packets of information are routed through a communication network using
a networking protocol such as the Internet Protocol (IP), which is a connnectionless
networking protocol. In a connectionless networking protocol, each packet of information
includes a network layer destination address, and each router forwards a packet of
information, based upon the network layer destination address, to the next router on the path.
The next router on the path to a particular network layer destination address is predetermined
by a routing protocol such as the Open Shortest Path First (OSPF) protocol, the Routing
Information Protocol(RIP), or other routing protocol.
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Each router makes an independent forwarding decision for the packet based upon its
analysis of the network layer destination address in the packet header. Each router determines
a next hop for each packet of information based upon the network layer destination address of
the packet, and forwards the packet of information to the corresponding next hop (or set of
hops) associated with the network layer destination address. Network layer routing, however,
requires that each router process each packets' information at the network layer. This
operation can be expensive (in terms of computing resources) and time consuming, and can
limit the performance of some routers.
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Alternatively, packets of information may be routed through a communication
network using label switching. Label switching allows a packet to be transported across a
network domain using labels rather than the network layer address. A label is a short, fixed
length value which represents an forwarding equivalence class ("FEC"). A Label Switched
Path (LSP) may be established from an ingress border device to an egress border device in the
network domain. The LSP traverses a number of label switching devices. Each label
switching device assigns a label to each FEC that it supports. When the packet enters the
ingress border device, the ingress border device analyzes the network layer and/or transport
layer header of the packet and assigns the packet to a particular FEC. The ingress border
device will then insert the corresponding label into the packet, either as a field in the layer 2
header, or as part of a new header inserted between the layer 2 and layer 3 header. Once a
packet is assigned a label (and thus an FEC) no further header analysis is done by subsequent
label switching devices. Each intermediate label switching device along the LSP makes its
forwarding decision for the packet using the label to determine the next hop label and output
port for the packet. Each intermediate label switching device will remove the label in the
packet and replace it with a label corresponding to the next hop on the label switched path.
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It is also possible for a packet to have more than one label (i.e., a label stack).
Typically, the label stack is a last-in, first-out stack. When a packet has a label stack, the set
of label operations will be the same, i.e., the packet is switched based on the top level of the
label stack, except that at some points a label switching device may remove and replace
multiple labels or remove the entire label stack. Label stacks allow hierarchical operation or
the use of multiple streams within a label switched path.
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The Internet Engineering task Force (IETF) Multi-Protocol Label Switching (MPLS)
working group has defined an MPLS architecture for utilizing label switching for
internetworking. MPLS is considered to be multi-protocol because it can be used with many
layer 2 protocols, such as ATM or frame relay, and with any network layer protocol, not just
IP. The framework for MPLS is described in an IETF Internet draft document entitled "A
Framework for MPLS," which is referenced as draft-ietf-mpls-framework-05.txt (September
1999), and is herein incorporated by reference in its entirety. The MPLS architecture is
described in an IETF Internet draft document entitled "Multiprotocol Label Switching
Architecture," which is referenced as draft-ietf-mpls-arch-06.txt (August 1999), and is hereby
incorporated by reference in its entirety.
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In order to use label switching for internetworking, each label switching device must
learn the labels that are used by its neighboring label switching device(s). Therefore, the
IETF MPLS working group has defined a Label Distribution Protocol (LDP) for distributing
labels between neighboring label switching devices. LDP may be used to distribute labels
between both contiguous and non-contiguous label switching devices. LDP is described in an
IETF Internet Draft document entitled "LDP Specification," which is referenced as draft-ietf-ldp-06.txt
(October 1999), and is hereby incorporated by reference in its entirety. There are
also other protocols used for label distribution known in the art.
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Each label switching device maintains a label information base (LIB) for mapping
each FEC to a corresponding label. When the label switching device receives a packet
including a label (or label stack), the label switching device utilizes the LIB to map the
received label (or the top label of the label stack) to a next hop label and port. The label
switching device then replaces the label (or the top label in the label stack) in the packet with
the label for the next hop, and forwards the resulting packet to the corresponding outgoing
path (or set of paths). In certain situations, when the label switching device is an egress
border device, the label switching device will remove the entire label stack.
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It may be desirable to set up an LSP which crosses multiple network domains. An
LSP which traverses multiple network domains may be desirable for traffic engineering
purposes. Traffic engineering is the process of selecting the paths followed by data traffic in
a computer network in order to balance the traffic load on the various links, routers, and
switches in the network with the goal of reducing congestion and optimizing the use of
network resources. MPLS may be used to implement explicitly routed paths to control where
the data traffic flows in the network. MPLS traffic engineering routes the traffic flows across
a network based on the resources the traffic flow requires and the resources available in the
network. Explicitly routed paths may be chosen at or before the time a packet enters the
network. In setting up an explicitly routed LSP, it may be desirable to select a route which
crosses a non-MPLS domain (i.e., a domain which contains non-MPLS compliant devices).
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However, if the network domains traversed by the LSP are not all MPLS domains
(i.e. a domain with MPLS compliant devices), any label stack information associated with the
packet will be lost when the packet enters the non-MPLS domain (i.e. a domain with non-MPLS
compliant devices). The last MPLS compliant device before the non-MPLS domain
(i.e., a border device) will remove the entire label stack from the packet before it is sent to the
non-MPLS domain. This is not a problem if the label stack includes only one label because
this label would be removed at the egress border device of the MPLS domain in any case.
However, if the depth of the label stack is greater than 1, all the information in the label stack
will be lost when the egress border device of the MPLS domain removes the label stack.
SUMMARY OF THE INVENTION
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In accordance with one aspect of the invention, a method for establishing a label
switched path for forwarding a packet and label stack in a communication network which
includes a first label switched domain and a second label switched domain interconnected by
a non-label switched domain includes establishing a tunnel across the non-label switched
domain which connects the first label switched domain and the second label switched
domain. The packet and label stack are encapsulated to form a tunnel packet and forwarded
through the tunnel. The tunnel may be an IP tunnel such as a Generic Routing Encapsulation
(GRE) tunnel. In one embodiment, the first and second label switched domains are
Multiprotocol Label Switching (MPLS) domains. In a further embodiment, the method
further includes providing an MPLS identifier in the tunnel packet such that the second label
switched domain may identify the packet and label stack.
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In accordance with another aspect of the invention a device for establishing a label
switched path for forwarding a packet and label stack in a communication network which
includes a first label switched domain and an second label switched domain interconnected by
a non-label switched domain includes label switching forwarding logic for analyzing the label
stack of the packet to determine the next hop for the packet. The device further includes
encapsulating logic for encapsulating the packet and label stack information to form a tunnel
packet and for establishing a tunnel across the non-label switched domain which connects the
first label switched domain and the second label switched domain. Forwarding logic forwards
the tunnel packet through the tunnel. The tunnel may be an IP tunnel such as a Generic
Routing Encapsulation (GRE) tunnel. In one embodiment, the first label switched domain
and the second label switched domain are Multiprotocol Label Switching (MPLS) domains.
In a further embodiment, the tunnel packet includes a MPLS identifier such that the second
label switched domain can identify the packet and label stack.
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In yet another embodiment, a method for establishing a label switched path for
forwarding a packet and label stack in a communication network which includes a first label
switched domain and an second label switched domain interconnected by a non-label
switched domain includes establishing a tunnel across the non-label switched domain which
connects the first label switched domain and the second label switched domain. A tunnel
packet comprised of an encapsulated packet and label stack is received from the tunnel. The
encapsulated packet and label stack are decapsulated and then forwarded across the second
label switched path.
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In a further embodiment, a device for establishing a label switched path for
forwarding a packet and label stack in a communication network which includes a first label
switched domain and an second label switched domain interconnected by a non-label
switched domain includes receiving logic for receiving a tunnel packet from a tunnel across
the non-label switched domain which connects the first label switched domain and the second
label switched domain, where the tunnel packet is comprised of an encapsulated packet and
label stack from the tunnel. The device further includes decapsulating logic for decapsulating
the encapsulated packet and label stack. Forwarding logic forwards the decapsulated packet
and label stack across the second label switched domain.
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In yet another further embodiment, a communication system is provided comprising a
first label switched domain having an egress device, a second label switched domain having
an ingress device and a non-label switched domain which couples the egress device of the
first label switched domain to the ingress device of the second label switched domain. In the
communication system a label path for forwarding a packet with a label stack is established
by establishing a tunnel from an egress device of the first label switched domain to an ingress
device of the second label switched domain over the non-label switched domain,
encapsulating the label switched packet by the egress device of the first label switched
domain, forwarding the encapsulated label switched packet by the egress device of the first
label switched domain over the tunnel to the ingress device of the second label switched
domain, decapsulating the encapsulated label switched packet by the ingress device of the
second label switched domain; and forwarding the decapsulated label switched packet by the
ingress device of the second label switched domain based upon label switching information in
the packet..
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Further embodiments of the invention are implemented as a computer program
product having a computer useable medium with computer readable program code thereon.
The computer readable code may be read and utilized by the computer system in accordance
with conventional processes.
BRIEF DESCRIPTION OF THE DRAWINGS
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The foregoing and other objects and advantages of the invention will be appreciated
more fully from the following further description thereof with reference to the accompanying
drawings wherein:
- Figure 1 is a schematic block diagram of a communication network label switched
path which includes a non-MPLS domain.
- Figure 2 is a schematic block diagram of a communication network label switched
path using an IP tunnel to cross a non-MPLS compliant section of the communication
network in accordance with an embodiment of the invention.
- Figure 3 illustrates the flow of control of a method for supporting a label switched
path across a non-MPLS compliant segment in accordance with an embodiment of the
invention.
- Figure 4 illustrates the flow of control of an egress device in a first label switched
domain along the label switched path in accordance with the embodiment of Figure 2.
- Figure 5 is a block diagram of an egress device in the first label switched domain
along the label switched path in accordance with the embodiment of Figure 2.
- Figure 6 illustrates the flow of control of an ingress device in a second label switched
domain along the label switched path in accordance with the embodiment of the Figure 2.
- Figure 7 is a block diagram of an ingress device in a second label switched domain
along the label switched path in accordance with the embodiment of the Figure 2.
-
DESCRIPTION OF PREFERRED EMBODIMENTS
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An embodiment of the invention establishes a tunnel across a non-MPLS domain in a
communication network that includes a first MPLS domain and a second MPLS domain
interconnected by the non-MPLS domain. An encapsulation technique is used to preserve
any label stack information associated with a packet forwarded along a label switched path
(LSP) which includes the non-MPLS domain. Specifically, the egress device of the first
MPLS domain, instead of removing the label stack, encapsulates the packet and label stack
before forwarding the packet and label stack to the first non-MPLS device of the LSP in the
non-MPLS domain. A delivery header of the encapsulated packet is used to determine the
next hop for the encapsulated packet along the tunnel in the non-MPLS domain. When the
encapsulated packet is forwarded to the ingress device of the second MPLS domain, the
ingress device decapsulates the packet and label stack. The packet and label stack are then
forwarded across the second MPLS domain using label switching.
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Figure 1 is a schematic block diagram of an exemplary prior art communication
network that includes two MPLS domains (101,112) interconnected by a non-MPLS domain
(106). An LSP is established from border router BR1(102) to border router BR4 (111). The
LSP shown in Figure 1 traverses three network domains specifically the first MPLS domain
(101), non-MPLS domain (106) and second MPLS domain (112). An LSP such as that
shown in Figure 1 is possible because LDP permits LDP peers (i.e., two label switching
devices which use LDP to exchange label/FEC mappings) to be non-contiguous label
switching devices. In Figure 1, border router BR2 (104) and border router BR3 (108) are
non-contiguous label switching devices. The first MPLS domain (101) includes border router
BR1(102), intermediate router R1 (103) and border router BR2(104). The non-MPLS domain
(106) includes router R2(105), router R3(107) and a number of other non-MPLS compliant
devices (not shown). The routers in the non-MPLS domain use a network routing protocol
such as, for example, IP to forward a packet. The second MPLS domain (112) includes border
router BR3(108), intermediate routers R4(109) and R5(110) and border router BR4(111).
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Border router BR1 (102) of the first MPLS domain (101) receives a packet with a
label stack to be sent over the LSP to border router BR4(111). Border router BR1(102)
processes the packet based upon the top label in the label stack and replaces the top label with
a label that corresponds to the next hop FEC of the packet. The packet is then forwarded by
border router BR1(102) to intermediate router R1(103). Intermediate router R1(103) receives
the packet and processes the packet using the top label of the label stack. Intermediate router
R1(103) then replaces the top label of the packet and forwards the packet to border router
BR2(104). Because border router BR2(104) is the edge MPLS device of the first MPLS
domain(101), border router BR2(104) removes the entire label stack from the packet before it
is forwarded to router R2(105) in the non-MPLS domain. At this point all of the label stack
information is lost. Border router BR2(104) forwards the unlabeled packet (without the label
stack) using the network layer destination address of the packet.
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In the non-MPLS domain (106), router R2(105) and any intermediate routers (not
shown) forward the unlabeled packet based upon the network layer destination address of the
packet. Router R3(107) forwards the unlabeled packet to border router BR3(108) of the
second MPLS domain(112). Border router BR3(108) analyzes the network layer header ( and
possibly the transport layer header) of the unlabeled packet to determine the next hop FEC for
the packet. Border router BR3(108) inserts a label or labels (i.e. a label stack) into the packet
header and forwards the packet to intermediate router R4(109). Forwarding of the packet
over the second MPLS domain (112) in the LSP continues using label switching until the
packet reaches border router BR4(111).
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As described above, when an LSP crosses a non-MPLS domain, the label stack
information associated with the packet delivered over the LSP will be lost when the packet
enters the non-MPLS domain. In order to preserve the label stack information of the packet,
an IP tunnel may be advantageously established to cross the non-MPLS domain. Figure 2 is a
schematic block diagram of a communication network LSP using an IP tunnel to cross a non-MPLS
compliant segment of an LSP in accordance with an embodiment of the invention. An
LSP is established between border router BR1(202) and border router BR4(208) which
crosses a non-MPLS domain (206). In a prior art embodiment, the label stack information of
a packet would be removed by border router BR2(204) before the packet is forwarded to a
router along the LSP in the non-MPLS domain (206). However, in an exemplary
embodiment of the invention as shown in Figure 2, an IP tunnel(210) is established across the
non-MPLS domain (206) to connect border router BR2 (204) of the first MPLS domain and
border router BR3(205) of the second MPLS domain. The IP tunnel may be a generic routing
encapsulation (GRE) tunnel. GRE is described in an IETF Request for Comments (RFC)
document entitled "Generic Routing Encapsulation (GRE)" [RFC1701 (October 1994)] and
an IETF Internet draft document entitled "Generic Routing Encapsulation (GRE)," which is
referenced as draft-meyer-gre-update-03.txt (January 2000), and are hereby incorporated by
reference in its entirety. The GRE tunnel (210) is used to encapsulate the entire packet
including the label stack information. The packet and label stack information may then be
sent across the non-MPLS domain through the GRE tunnel (210). In one embodiment, the
current implementation of the GRE protocol as described in the above-referenced documents
may be modified. Specifically, the GRE protocol would be amended to make MPLS a
supported GRE payload packet protocol type. This amendment would require assigning a
reference number to the MPLS protocol which a GRE header would carry in its protocol type
field.
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Returning to Figure 2, after the GRE tunnel (210) has been established, a GRE header
is prepended to the packet and label stack (i.e., the payload packet). The GRE header
includes information such as the protocol type of the payload packet. A protocol type
identifier corresponding to MPLS is inserted in the GRE header so that-border router
BR3(205) can identify the packet and process the packet based upon the MPLS label stack.
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The GRE packet (i.e., the payload packet and GRE header) is then encapsulated in a
delivery header (such as an IP header) and forwarded across the non-MPLS domain. Each
router (not shown) in the non-MPLS domain (206) forwards the GRE packet using the IP
header. When the GRE packet reaches border router BR3(205) of the second MPLS domain
(209), the border router BR3(205) removes the IP and GRE headers and process the payload
packet (i.e. the original packet and label stack) using the label stack, Border router BR3(205)
places a new label onto the label stack corresponding to the next hop FEC of the packet.
Forwarding of the packet across the second MPLS domain (209) continues using label
switching until the packet reaches border router BR4(208). In alternative embodiments of the
invention, other IP tunnel types such as Layer Two Tunneling Protocol (L2TP), Layer Two
Forwarding (L2F), User Datagram Protocol (UDP) and IP Security (IPSEC) may be used for
the IP tunnel (210). Each of these protocol types would require appropriate protocol specific
modifications in order to support MPLS as a payload packet protocol type.
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Figure 3 illustrates the flow of control of a method for supporting a label switched
path across a non-MPLS compliant segment in accordance with an embodiment of the
invention. At block 301, an LSP is established which traverses multiple network domains,
specifically, a first MPLS domain and a second MPLS domain interconnected by a non-MPLS
domain. As discussed above, label stack information associated with a packet
typically would be removed, in a prior art embodiment, when a packet with a label stack is
forwarded from the first MPLS domain to the non-MPLS domain. In order to preserve the
label stack information in the packet, at block 302, an IP tunnel is established which crosses
the non-MPLS domain and connects the first MPLS domain to the second MPLS domain of
the LSP. As discussed above, the IP tunnel may be a GRE tunnel. At block 303, a packet
with a label stack is forwarded across the first MPLS domain using label switching until the
packet reaches the non-MPLS domain. When the packet reaches the non-MPLS domain, the
packet and label stack(the payload packet) are encapsulated at block 304. A GRE and IP
header are placed on the payload packet to form a GRE packet. In addition, a payload packet
identifier corresponding to MPLS is placed in the GRE header. At block 305, the GRE
packet is then sent across the non-MPLS domain through the GRE tunnel. When the GRE
packet reaches the second MPLS domain of the LSP, the IP and GRE headers of the GRE
packet are removed at block 306 and the payload packet is forwarded across the second
MPLS domain using label switching at block 307. By using the IP tunnel, the label stack
information of the packet is preserved as it crosses the non-MPLS domain of the LSP. In
alternative embodiments of the invention, the IP tunnel may be a L2TP, L2F, UDP or IPSEC
tunnel.
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Figure 4 illustrates the flow of control of an egress device in the first label switched
domain along the label switched path (LSP) in accordance with the embodiment of Figure 2.
Stalling at block 402, the egress device (such as border router BR2 as shown in Figure 2 )
receives a packet with a label stack from the previous label switching device in the LSP at
block 404. The egress device then analyzes the top label of the packet to determine the
forwarding for the packet in block 406. If the LSP traverses the non-MPLS domain, then the
next hop for the LSP is mapped to an ingress border device of the non-MPLS domain. The
mapping also indicates that the packet should be encapsulated before being forwarded to the
non-MPLS domain. In other words, the packet label will infer a mapping of the label to the
tunnel across the non-MPLS domain.
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Once the egress device has determined the forwarding for the packet, in this case to
the tunnel across the non-MPLS domain, the egress device removes (or pops) the top label
from the label stack of the packet at block 408. At block 410, the packet and label stack are
encapsulated. As described above, in one embodiment, the packet and label stack are
encapsulated using GRE. Once the packet and label stack are encapsulated, the encapsulated
packet is forwarded to the next hop device in the non-MPLS domain using the encapsulation
header at block 412. The logic terminates at block 414.
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Figure 5 is a block diagram of an egress device 500 in the first label switched domain
along the label switched path in accordance with the embodiment of Figure 2. The egress
device 500 includes receiving logic 502 for receiving a packet with a label stack from the
previous label switching device in the label switched path. Label switching forwarding logic
504 is used to analyze the top label of the label stack to determine the next hop for the packet.
The label switching forwarding logic 504 identifies that the next hop is in the non-MPLS
domain and that the packet and label stack should be encapsulated before being forwarded.
Encapsulation logic 506 is then used to encapsulate the packet and label stack for delivery
along a tunnel across the non-MPLS domain. IP forwarding logic 508 forwards the
encapsulated packet to the next hop device in the non-MPLS domain.
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Figure 6 illustrates the flow of control for an ingress device of the second label
switched domain along the label switched path in accordance with the embodiment of Figure
2. Starting at block 600, the ingress devices receives an encapsulated packet from the last
non-MPLS device of the tunnel across the non-MPLS domain at block 602. The packet is
analyzed to identify the payload packet protocol as MPLS using an identifier in the header of
the encapsulated packet at block 604. At block 606, the encapsulation headers are removed
from the encapsulated packet leaving only the original packet and label stack. At block 608,
the ingress device forwards the packet and label stack based on the top label of the label
stack. The ingress device will place a label on the label stack corresponding to the next hop
for the packet. The packet and label stack are forwarded to the next hop label switching
device along the LSP in the second MPLS domain. The logic terminates at block 610.
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Figure 7 is a block diagram of an ingress device 700 in a second MPLS domain along
the label switched path in accordance with the embodiment of Figure 2. The ingress device
700 includes receiving logic 702 for receiving an encapsulated packet from the last non-MPLS
device of the tunnel across the non-MPLS domain. Demultiplexing logic 704
identifies the payload packet protocol as MPLS using an identifier in the header of the
encapsulated packet. Decapsulation logic 706 removes the encapsulation headers from the
encapsulated packet leaving the original packet and label stack. Label switching forwarding
logic 708 then forwards the packet to the next hop label switching device of the LSP in the
second MPLS domain based on the top label of the packet.
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In a preferred embodiment of the invention, predominantly all of the logic for
supporting a label switched path across a non-MPLS compliant segment is implemented as a
set of computer program instructions that are stored in a computer readable medium and
executed by an embedded microprocessor system within the router. Preferred embodiments
of the invention may be implemented in any conventional computer programming language.
For example, preferred embodiments may be implemented in a procedural programming
language (e.g., "C") or an object oriented programming language (e.g., "C++"). Alternative
embodiments of the invention may be implemented using discrete components, integrated
circuitry, programmable logic used in conjunction with a programmable logic device such as
a Field Programmable Gate Array (FPGA) or microprocessor, or any other means including
any combination thereof.
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Alternative embodiments of the invention may be implemented as a computer
program product for use with a computer system. Such implementation may include a series
of computer instructions fixed either on a tangible medium, such as a computer readable
media (e.g., a diskette, CD-ROM, ROM, or fixed disk), or fixed in a computer data signal
embodied in a carrier wave that is transmittable to a computer system via a modem or other
interface device, such as a communications adapter connected to a network over a medium.
The medium may be either a tangible medium (e.g., optical or analog communications lines)
or a medium implemented with wireless techniques (e.g., microwave, infrared or other
transmission techniques). The series of computer instructions preferably embodies all or part
of the functionality previously described herein with respect to the system. Those skilled in
the art should appreciate that such computer instructions can be written in a number of
programming languages for use with many computer architectures or operating systems.
Furthermore, such instructions may be stored in any memory device, such as semiconductor,
magnetic, optical or other memory devices, and may be transmitted using any
communications technology, such as optical, infrared, microwave, or other transmission
technologies. It is expected that such a computer program product may be distributed as a
removable medium with accompanying printed or electronic documentation (e.g., shrink
wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk),
or distributed from a server or electronic bulletin board over the network (e.g., the Internet or
World Wide Web).
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It should be noted that the term "packet" is used herein generically to describe various
protocol messages that are processed by a communication device, and should not be
construed to limit application of the present invention to a specific protocol message format
or communication protocol. Thus, a "packet" may be any protocol message including, but
not limited to, a frame, a packet, a datagram, a user datagram or a cell.
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It should also be noted that the terms "router" and "switch" are used herein generically
to describe any of a variety of devices that implement the described protocols and procedures
for supporting a LSP across a non-MPLS segment, and should not be construed to limit
application of the present invention to any specific type of device.
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It should be noted that, although the present invention utilizes IETF Label
Distribution Protocol ("LDP") for distributing labels between various label switching devices,
the mechanism described herein can be applied more generally to other protocols, including,
but not limited to, various embodiments of the IETF LDP as currently defined or hereinafter
revised. The present invention is in no way limited to the IETF LDP.
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It should also be noted that, although the present invention utilizes IETF Multi-Protocol
Label Switching ("MPLS") for utilizing label switching for internetworking, the
mechanism described herein can be applied more generally to other label switching protocols,
including, but not limited to, various embodiments of the IETF MPLS as currently defined or
hereinafter revised. The present invention is in no way limited to the IETF MPLS.
-
It should be noted that, although a preferred embodiment of the invention uses
Generic Routing Encapsulation ("GRE") protocol for tunneling, the mechanism described
herein can be applied more generally to other tunneling protocols. The present invention is in
no way limited to GRE.
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Thus, the present invention may be embodied as a method for establishing a label
switched path for forwarding a packet with a label stack in a communication network which
includes a first label switched domain and a second label switched domain interconnected by
a non-label switched domain. The method involves establishing a tunnel across the non-label
switched domain which connects the first label switched domain and the second label
switched domain, encapsulating the packet and label stack to form a tunnel packet and
forwarding the tunnel packet through the tunnel.
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The present invention may be embodied as a device for establishing a label switched
path for forwarding a packet with a label stack in a communication network which includes a
first label switched domain and a second label switched domain interconnected by a non-label
switched domain. The device includes label switching forwarding logic for analyzing the
label stack of the packet to determine the next hop for the packet, encapsulating logic for
encapsulating the packet and label stack to form a tunnel packet and for establishing a tunnel
across the non-label switched domain which connects the first label switched domain and the
second label switched domain, and forwarding logic for forwarding the tunnel packet through
the tunnel.
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The present invention may also be embodied as a computer program product
comprising a computer readable medium having embodied therein a computer program for
establishing a label switched path for forwarding a packet with a label stack in a
communication network which includes a first label switched domain and a second label
switched domain interconnected by a non-label switched domain. The computer program
includes program code establishing a tunnel across the non-label switched domain which
connects the first label switched domain and the second label switched domain, program code
for encapsulating the packet and label stack to form a tunnel packet and program code for
forwarding the tunnel packet through the tunnel.
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The present invention may be embodied as a communication system including a first
label switched domain having an egress device, a second label switched domain having an
ingress device and a non-label switched domain which couples the egress device of the first
label switched domain to the ingress device of the second label switched domain where a
label switched path for forwarding a packet with a label stack is established by establishing a
tunnel from an egress device of the first label switched domain to an ingress device of the
second label switched domain over the non-label switched domain, encapsulating the label
switched packet by the egress device of the first label switched domain, forwarding the
encapsulated label switched packet by the egress device of the first label switched domain
over the tunnel to the ingress device of the second label switched domain, decapsulating the
encapsulated label switched packet by the ingress device of the second label switched domain
and forwarding the decapsulated label switched packet by the ingress device of the second
label switched domain based upon label switching information in the packet.
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Although various exemplary embodiments of the invention have been disclosed, it
should be apparent to those skilled in the art that various changes and modifications can be
made which will achieve some of the advantages of the invention without departing from the
true scope of the invention. These and other obvious modifications are intended to be
covered by the appended claims.